Hydrogeochemical characteristics and water-rock interaction mechanism of coalbed-produced water in the Linfen mining area, eastern margin of Ordos Basin, China

Linfen mining area is one of the main coalbed methane industrial bases in the eastern margin of Ordos Basin, China. However, there are few studies on the hydrogeochemical characteristics of coalbed-produced water in the area. This article collected water samples from 14 coalbed methane drainage wells and analyzed the ionic concentrations, hydrogen and oxygen isotopes, dissolved inorganic carbon isotopes (δ13CDIC) and trace elements. The results showed that the water of Nos. Five and eight coal seams are both Cl-Na type. The total dissolved solids content was high, ranging from 5011.45 mg/L to 23405.39 mg/L. Hydrogen and oxygen isotope data indicated that the coalbed-produced water in the study area is recharged from atmospheric precipitation. In addition, the HCO3− in the produced water of No. Five coal seam and No. Eight coal seam was negatively correlated with δ13CDIC. The value δ13CDIC in the produced water of No. Five coal seam was heavier than that of No. Eight coal seam. These indicate that microbial degradation occurred more strongly in No. Five coal seam than in No. Eight coal seam. The water-rock interaction in the study area was found to be dominated by cation exchange and dissolution filtration through the relationships between anion and cation.